Adding additional IsGitHubDotCom method

Author: StanleyGoldman

src/GitHub.Api/Application/ApiClient.cs

@@ -205,7 +205,7 @@ public async Task<bool> ContinueLoginAsync(LoginResult loginResult, Func<LoginRe
             // it'll throw if it's private or an enterprise instance requiring authentication
             catch (ApiException apiex)
             {
-                if (!HostAddress.IsGitHubDotComUri(OriginalUrl.ToRepositoryUri()))
+                if (!HostAddress.IsGitHubDotCom(OriginalUrl.ToRepositoryUri()))
                     isEnterprise = apiex.IsGitHubApiException();
             }
             catch {}

src/GitHub.Api/Authentication/LoginManager.cs

@@ -257,7 +257,7 @@ bool EnterpriseWorkaround(UriString hostAddress, Exception e)
             // the failure, using basic authentication (with username and password) instead of trying
             // to get an authorization token.
             var apiException = e as ApiException;
-            return !HostAddress.IsGitHubDotComUri(hostAddress.ToUri()) &&
+            return !HostAddress.IsGitHubDotCom(hostAddress) &&
                 (e is NotFoundException ||
                  e is ForbiddenException ||
                  apiException?.StatusCode == (HttpStatusCode)422);

src/GitHub.Api/Primitives/HostAddress.cs

@@ -16,7 +16,7 @@ public class HostAddress
         /// <returns></returns>
         public static HostAddress Create(Uri hostUri)
         {
-            return IsGitHubDotComUri(hostUri)
+            return IsGitHubDotCom(hostUri)
                 ? GitHubDotComHostAddress
                 : new HostAddress(hostUri);
         }
@@ -68,16 +68,26 @@ public HostAddress()
         // since that's the same cache key for all the other github.com operations.
         public string CredentialCacheKeyHost { get; private set; }
 
-        public static bool IsGitHubDotComUri(Uri hostUri)
+        public static bool IsGitHubDotCom(Uri hostUri)
         {
             return hostUri.IsSameHost(GitHubDotComHostAddress.WebUri)
                    || hostUri.IsSameHost(GitHubDotComHostAddress.ApiUri)
                    || hostUri.IsSameHost(gistUri);
         }
 
+        public static bool IsGitHubDotCom(string url)
+        {
+            if (String.IsNullOrEmpty(url))
+                return false;
+            Uri uri = null;
+            if (!Uri.TryCreate(url, UriKind.Absolute, out uri))
+                return false;
+            return IsGitHubDotCom(uri);
+        }
+
         public bool IsGitHubDotCom()
         {
-            return IsGitHubDotComUri(ApiUri);
+            return IsGitHubDotCom(ApiUri);
         }
 
         public string Title